1. Field of the Invention
The present invention relates to a fan rotation speed control technique.
2. Description of the Related Art
A fan is a common heat-dissipating device, which produces air flow to remove heat from components, such as central processing units (CPU), which generate heat but are temperature sensitive, to control the temperature variation thereof to within a specific range.
FIG. 1 is a schematic diagram of a heat-dissipating configuration in a laptop computer for illustrating how the prior art controls a heat-dissipating fan for the CPU in the laptop computer. The laptop computer 100 comprises a CPU 110, an embedded controller (EC) 120, a fan rotation speed controller 130, and a fan 140. The fan 140 produces air flow by rotating its blades (not shown) to remove heat accumulated by the CPU 110. The EC 120 continually monitors the temperature of the CPU 110 with temperature sensors (not shown), and outputs signal values, which may be in a specific coded form, to the fan rotation speed controller 130. Then, the fan rotation speed controller 130 linearly adjusts the driving voltage outputted to the fan 140 based on the signal value received from the EC 120 to control the rotation speed of the fan 140. At the same time, the fan rotation speed controller 130 receives information about the actual rotation speed of the fan 140 and reports it to the EC 120. Note that, in the prior art, the signal values outputted from the EC 120 run in “progression”. For illustration, in the following examples, the signal values are hexadecimal codes ranging from (00) to (FF). When the EC 120 finds out that the actual rotation speed reported by the fan rotation speed controller 130 has not reached the target rotation speed (for example, the signal value 79), the next signal value sent by the EC 120 will increase by 1 (i.e., increasing from signal value 79 to signal value 7A) and then the process goes on and on till the actual rotation speed reaches the target rotation speed. Oppositely, when the EC 120 finds out that the actual rotation speed reported by the fan rotation speed controller 130 has exceeded the target rotation speed (for example, signal value 8F), the next signal value sent by the EC 120 will decrease by 1 (i.e., decreasing from signal value 8F to signal value 8E) and then the process goes on and on till the actual rotation speed returns to the target rotation speed.
For a computer system, the fans integrated therein may be from different sources (vendors), such that they may have different voltage-rotation speed characteristics. Therefore, an EC in a computer system should increase or decrease the signal value progressively and adjust the fan driving voltage gradually. However, for the prior art methods, a lot of time is needed for a fan to reach a target rotation speed (for example, if the EC 120 sends a signal value every second, and the signal value increases from 79 to 8E, it takes 20 seconds). In addition, for the prior art methods, it is difficult to control the fan to rotate at a stable rotation speed. A fan rotating too fast may cause noise and waste power, while a fan rotating too slowly may reduce the heat dissipation effect. Accordingly, the quality of a computer system may decrease.
Fan rotation speed control in the prior art is neither effective nor precise. Therefore, the present invention overcomes the defects in the prior art and provides a new system and method for controlling the fan rotation speed.